Recording/reproducing devices typically comprises a rotatable disk media structure which includes a disk powered by a disk spindle motor, and, an actuator structure which comprises a transducer/actuator arm assembly on a movable support and powered by an actuator motor, for moving the transducer radially of the disk. The actuator may be either of the rotary or linear type and functions under servo controlled actuator motor power to move the transducer to different radial positions on a disk. In a disk drive this mode of operation is referred to as a track seeking and track following operation.
In a disk drive, the memory disk structure comprises one or more disks in a memory disk assembly, concentrically mounted about a disk spindle hub which is driven by a radial gap disk spindle motor having a stator mounted to the base of the disk drive housing. In the memory disk assembly, one or more disks are clamped in a stack about the disk spindle hub, multiple disks being axially spaced by ring spacers of sufficient thickness to space the disks to clear individual actuator structures therebetween. The stator of the disk spindle motor is assembled within the disk spindle hub. The disk spindle hub functions as the motor rotor.
As disk drives are reduced in size, such motor designs in the memory disk structure become impractical in both radial and axial dimension. As the radius is reduced adequate motor torque is no longer available. Design efforts to increase motor torque by increasing the radius of the motor and reducing the axial dimension, have resulted in radial gap disk spindle motors having relatively thin-flat, rotors of sufficient diameter so that motor torque requirements may be met. The stator structure with its windings is disposed within the motor rotor. The large diameter of the motor rotor of this type of disk spindle motor, in relation to the dimension of the memory disk(s), prevents its disposition within the memory disk stack, so the memory disk(s) and the disk spindle motor are axially stacked. This motor design has a low profile and has resulted in improvement in motor torque. The design requires the axial stacking of the disk spindle motor and the memory disk(s), rather than concentrically disposing the disk stacks about the motor, consequently there is some loss in volumetric efficiency. There remains not only a need for further reductions in the thickness or profile of the disk spindle motor but also a need to reduce the thickness of the recording/reproducing device.